Internal combustion engines combust an air and fuel mixture to generate drive torque. More specifically, air is drawn into the engine and is mixed with fuel. The air and fuel mixture is combusted within cylinders to drive a crankshaft, producing drive torque. Mass airflow into the engine and the quantity of fuel injected determine the amount of drive torque generated.
Some engines include exhaust gas recirculation (EGR) systems to improve engine operation and reduce engine emissions. The EGR system includes an EGR valve that regulates an amount of exhaust gas that is circulated back to the intake manifold. The additional exhaust gas affects the amount of engine air intake through the throttle. EGR is the most efficient means to reduce overall emissions. Large amounts of EGR (e.g., up to 60%) may be necessary to sufficiently reduce the emissions to meet regulatory requirements.
During transient maneuvers, the required amount of EGR and the actually achieved EGR may differ as a result of delays in the engine system. In some cases, the difference could be quite significant, which can result in an unacceptable increase in emissions (i.e., NOx and HC) during transient maneuvers.